1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Along with the recent miniaturization of semiconductor devices, the current drive capability of a field effect transistor composing a semiconductor device tends to degrade. In order to enhance this current drive capability, there has been proposed a vertical field effect transistor including a three-dimensional structure in which a source region, a channel region and a drain region are vertically arranged. This vertical field effect transistor has the advantage that it is possible to achieve a dramatic enhancement in the current drive capability by completely depleting the channel region.
A conventionally used vertical field effect transistor includes a silicon column in which source/drain regions and a channel region are formed. This channel region is surrounded by a gate insulating film and a gate electrode. The source/drain regions are formed in the upper and lower portions of the silicon column. Thus, the vertical field effect transistor has a structure in which the channel region is completely covered with the source/drain regions.
In addition, this vertical field effect transistor is used in a wide variety of fields for its advantages. For example, the vertical field effect transistor is used as a transistor for a memory cell of a DRAM. Japanese Patent Laid-Open No. 2005-260014 discloses a semiconductor device including a plurality of memory cells disposed at intersection points where a plurality of word lines and a plurality of bit lines intersect. Each of these memory cells includes a vertical field effect transistor in which a channel region is formed in the depth direction of the memory cell, and a memory element the resistance value of which changes according to a temperature applied to either the upper or lower portion thereof.
The present inventor has recognized that the present invention provides a semiconductor device including a bit line and a word line and at least part of a bit line and a word line is made of a metal material.